Re: Running for an external HDD
you dont need to install Ubuntu/Kubuntu in seperate partitions. you can install Ubuntu and then kubuntu-desktop or first install Kubuntu and then install ubuntu-desktop package for the same effect.
when you login make sure you choose the session type as GNOME or KDE for Ubuntu and Kubuntu respectively. they are the same OS only different desktop environments.
that way you can try both and choose what works for you. also you can pick and choose apps running KDE apps in GNOME and vice versa
Refugee from openSuse ever since they sold out to M$